1. Field of the Invention
The present invention generally relates to a voltage generating apparatus, and in particular, to a voltage generating apparatus with a temperature compensation capability.
2. Description of Related Art
In the current electronic products, there are always some irreplaceable analog circuits. Most of the analog circuits may require an accurate reference power supply for achieving a stable behaviour. Thus, many so-called band gap voltage generating apparatuses are introduced. The most important subject matter of these band gap voltage generating apparatuses is a self-compensation capability of the output voltage for a temperature change.
Referring to FIG. 1, a circuit diagram of a conventional voltage generating apparatus 100 with a temperature compensation capability is shown. The voltage generating apparatus 100 generates currents I1 and 12 by using a transistor M1 and a transistor M2, respectively. The current I1 is divided into a current I1a and a current I1b, while the current I2 is divided into a current I1a and a current I2b. The current I1b flows through a bipolarity transistor Q1 and generates a voltage VEB1, and likewise, the current I2b flows through the bipolarity transistor Q2 and generates a voltage VEB2. An amplifier AMP1 receives the above voltages VEB1, VEB2, and generates a band gap voltage VBG through an output consisting of a transistor M3 and a resistor R1.
This band gap voltage VBG has a positive temperature coefficient, so for achieving a compensation effect, a set of low pass filters 101 is connected in series behind the band gap voltage VBG in the voltage generating apparatus 100. The low pass filter 101 consisting of a capacitor and a resistor has a negative temperature coefficient, and thus, may efficiently generate a temperature compensation effect to the output voltage Vout, so that the output voltage Vout would not drift as the temperature changes.
However, the above voltage generating apparatus 100 has to use a particular number of capacitors and resistors, thus increasing the circuit area and cost. Furthermore, the architecture of this conventional voltage generating apparatus cannot increase both the power swing rejection ratio (PSRR) and the bandwidth, thus influencing the whole behaviour.